Portable computing devices, such as mobile phones, portable and tablet computers, entertainment devices, handheld navigation devices, and the like increasingly offer more functions and features which can make it difficult for a user to navigate and select commands that are relevant to a function the user wants to initiate on a device. In addition to the traditional techniques used to interact with computing devices, such as a mouse, keyboard, and other input devices, touch sensors and touch-screen displays are commonly integrated in mobile phones and tablet computers, and are utilized both for display and user-selectable touch and gesture inputs. A continuing design challenge with these types of portable devices having touch sensors and/or touch-screen displays is the touch signal processing to track touch and gesture inputs that are identified from successive frames of sensor image data. Touch contacts on a touch-screen display represent the motion trace of a gesture, such as when a user uses his or her fingers to contact a touch-screen display and gesture while maintaining the contact with the display. A failure to correctly track and interpret the motion trace of a touch contact for a gesture input can lead to the failure of gesture recognition operations and gesture tracking processing.
For a gesture motion that is a relatively small or short gesture, conventional tracking processing may statically match the spatially co-located touch contacts from successive frames. However, this approach is not effective for a gesture motion that is a relatively large or long gesture, such as may be typically used on a tablet computer or other type of slate form factor where fast gestures such as flicker or panning are involved. The tracking processing may not be sensitive to the complete motion of a gesture, which can result in a gesture “break”, which may then be recognized and processed as much shorter motion ranges than the actual gesture motion. Alternatively, if the tracking processing is overly sensitive to the gesture motion, this can lead to mis-tracking the touch contacts, such as when a user inputs text with a soft or virtual keyboard that is displayed on a touch-screen display.